Reversal of LPS-induced immobility in mice by green tea polyphenols: possible COX-2 mechanism

An endotoxin (lipopolysaccharide, LPS) is known to activate the hypothalamo-pituitary adrenocortical axis, as well as norepinephrine and indolamine metabolism. Systemically administered LPS produces depression in the forced swimming-induced despair behaviour model in mice. The present study was designed to investigate the effect of green tea extract (GTE) on LPS-induced despair behaviour and to explore the mechanism involved in modulation of LPS-induced immobility by GTE. GTE (10-100 mg/kg) pretreatment reversed LPS-induced immobility in a dose-dependent manner. Rofecoxib (2 mg/kg) and nimesulide (2 mg/kg), COX-2 inhibitors, also reversed the LPS-induced immobility, which was significantly potentiated by concomitant administration of GTE. On the other hand, GTE did not show any potentiating effect on immobility with naproxen (10 mg/kg), which is a nonselective COX blocker. Interestingly the antioxidant, carvedilol (2 mg/kg) did not produce any effect on immobility either in normal or in LPS treated mice. The results of the study implicate the role of COX-2 inhibition by GTE in the reversal of LPS-induced immobility.